Opponents of passing a new Iran sanctions bill got a boost from two foreign policy luminaries on Wednesday: former national security advisers Brent Scowcroft and Zbigniew Brzezinski.

Both came out against a new sanctions bill during appearances at a Wednesday Senate Armed Services Committee hearing, saying the new legislation would damage talks with Iran on curbing that country’s nuclear program.

“They will break the talks,” said Scowcroft, who served as national security adviser under Republican Presidents Gerald Ford and George H.W. Bush. “I think we should see them out and not take steps which would destroy the negotiations.”“I have a similar perspective,” said Brzezinski, who served as national security adviser under Democratic President Jimmy Carter. “Iran is beginning to evolve.”

Sens. Bob Menendez (D-N.J.) and Mark Kirk (R-Ill.) are leading a push in the Senate to renew sanctions on Iran if the country walks away from negotiations, or violates the terms of an agreement.

The White House vehemently opposes such a bill, arguing it will derail current negotiations with Iran to reach a comprehensive deal to roll back Iran's nuclear program. The president issued another veto threat against sanctions legislation during his State of the Union address on Tuesday.

The Senate Banking Committee could debate and vote on a Kirk-Menendez bill next week, but Democrats are engaged in a heavy debate over whether to support the legislation at this time.

The Senate’s 54 Republicans would have to win over 13 Democrats to get to the 67 votes necessary to override a veto.

Support from all Republicans is not certain either. Sen. Bob Corker (R-Tenn.), chairman of the Senate Foreign Relations Committee, has proposed an alternative bill that would allow Congress to vote up or down on the final deal.

Sens. Barbara Boxer (D-Calif.) and Rand Paul (R-Ky.), a possible candidate for the White House in 2016, proposed legislation Wednesday that would restore previously lifted sanctions if Iran violates the terms of a future deal.

Scowcroft urged lawmakers to wait on passing any sanctions bill before the talks are due to conclude on June 30.

“I think we're on the homestretch. I think to change our strategy now might work, but I wouldn't do it at this stage,” he said.

Opponents of a new sanctions bill argue that adding sanctions would break cohesion among international allies participating in talks with Iran.

“Don't forget that we're not the only negotiators on Iran,” Brzezinski warned.